Is the leica super elmar m 21mm f 3 4 asph worth buying used?

Here is what the site says about that.

From Leica Super-Elmar-M 21mm f/3.4 ASPH: Leica Super-Elmar-M 21mm f/3.4 ASPH: A prime lens by Leica for Full frame cameras, 21mm f/3.4. A small 21mm; needs an external finder, live view or an EVF. Specs - Maker: Leica - Focal length: 21mm (prime) - Maximum aperture: f/3.4 - Made for: Full frame sensors - Mounts: Leica M - Stabilised: no - Autofocus: no, manual focus What it frames like - On full frame (Leica M): as marked, 21mm. Cameras it fits ...

From Leica Super-Elmar-M 18mm f/3.8 ASPH: Leica Super-Elmar-M 18mm f/3.8 ASPH: A prime lens by Leica for Full frame cameras, 18mm f/3.8.

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